Cylinders for lithographic printing machines

ABSTRACT

The invention provides a lithographic printing cylinder with an equi-atomic electrodeposited tin-nickel surface, and a method of printing employing such a cylinder.

United States Patet 1 1111 3,901,147

Holland 1 Aug. 26, 1975 CYLINDERS FOR LITHOGRAPHIC [56] References Cited PRINTING MACHINES UNITED STATES PATENTS [75] Inventor: Norman Holland, Hemel 2,004,824 6/1935 MacLcan 101/458 Hempstead, England 2,181,111 11/1939 Horn 101/458 2297,929 10 1942 Wise 101/454 1 Asslgneei Addressograph Mulllgraph 3,094,065 6/1963 11660118..v 101/148 Corporation, Cleveland.0h10 3168.457 2/1965 Grazcn 101/4011 x 3.232.718 2 1966 Scyb ct a1. 29/1964 x [22] June 1973 3,295,936 1/1967 Hidejiro at al 1. 29/1964 x [21} App]. No; 370,890

Related US Application Data Primary Examiner-C1yde I. Coughenour Attorney, Agent, or FirmRussell L. Root; Ray S. Pyle [63] Continuauon of Sun No. 143,203 May 13, 1971,

abandoned.

. 57 ABSTRACT US The invention provides a lithographic printing cylinder 101/45 with an equi-atomic electrodeposited tin-nickel sur- [5]] Int. Cl. face and a method of printing employing such a ylin- [58] Field of Search 29/130, 132; 101/148, 454, d

4 Claims, N0 Drawings CYLINDERS FOR LITI-IOGRAPIIIC PRINTING MACHINES This is a continuation, of application Serial No. 143,203 filed May 13, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to cylinders for printing machines. i v

The lithographic printing process makes one of a master having image areas which will accept a greasy ink and non-image areas which are wet and repel the ink. In present-day machines the master is mounted on a master cylinder and the'non-image areas kept in an ink repelling condition by moistening with an aqueous solution picked up from a moisture fountain by a set of moisture rolls. The master is inked, the ink being taken up by the image areas only, and printing then takes place either directly from the master cylinder or through an offset cylinder. The master cylinder must not accept ink; the moisture rolls must alsofnot accept ink, and also should be good carriers of the solution.

Lithographic master cylinders hitherto have been commonly of hard chromium-plated cast iron. The chromium surface is normally pr'epared after plating by reverse etching in a plating bath, or by re-plating with a flash" of chromium, i.e. a short duration high current intensity plating step. Asa result of this preparation the chromium surface is able to maintain a thin unbroken moisture layer, which gives it the desired oleophobic property. I I J y A typical assembly of moisture rolls comprises a knurled aluminium roller,a .n1 olleton (woyen textile surfaced) roller, a plain aluminium roller and a further molleton roller acting on the master cylindenThe aluminium rolls should be in polishedcondition since the usual oxide coating on aluminium tends to accept ink: for this reason the metal .,,rn oisture. rolls need to be cleaned frequently in. use. V I

For some time there has been commercially available a process for producing mastersfor lithographic printing: the master is produced photographically after which normal lithographic printing or copying from the master takes place. The stop bath in the photographic process commonly includescut phosphoric, acid and it has been found that this adversely affects the master cylinder. It is usual for the stop bath chemicals sooner or later to penetrate the chromium plating on the master roll and corrode both the chromium and the cast iron beneath it. The resultant pitting; which can be A; inch deep, renders the cylinder unfit for further service. Also, the moisture supplied during the printing contains salts which ionize-to produce further corrosive action.

Faced with the problem of frequent cylinder replacements the reaction of the industry has been to increase the thickness of chromium plating. While this increases average cylinder life to some extent it also increases the cost of the cylinders.

SUMMARY OF THE INVENTION The present invention is based on the discovery that the tin-nickel plating process can be made to produce a surface on a master cylinder which has properties superior to hard chromium plating without being unacceptably expensive. The tin-nickel plating process is of course one of a vast number of plating processes. Its

choice is surprising inter alia in that a tin-nickel plated surface as ordinarily produced is not hydrophilic but rather the reverse. Indeed what is understood to be the main use of Kingdom process in the United Kingdon at present is for plating automative brake cylinders. The plating absorbs the synthetic oils constituting the hydraulic fluid and is thus believed to minimize stiction (initial frictional resistance to movement); I g i It has been foundby the present inventor, however, that a tin-nickel plated surfacecan rendered or maintained hydrophilic by appropriate treatment. The process is less costly than chromium plating, requires no. back etch or. flash plating, and, gives .a surface which is much better resistant than chromium to stop bath corrosion. I

The inventor has also discovered that tin-nickel plated rolls with their surface hydrophilic can advantageously replace the aluminium .rolls in a train of moisture rolls. The tin-nickel surface holds a surprisingly. even layer of moisture, which promotes the even application of moisture to themaster'cylinder on which quality printing depends. Also, the tin-nickel surface does not require constant cleaning as do the aluminium rolls hitherto used.

The invention accordingly comprises a lithographic cylinder (which term is understood to include both a master cylinder and a moisture fountain roll) which has" a tin-nickel surface. The invention comprises als'o ifa:

process for producing such a surface. V i

I Th oug h a tin-nickel surface which has bee jn to dry out can be made hydrophilic'iby an etching step, in a preferredforrn of the invention, the surface after formation and before it has dried is coated with a we:

servative, e.g. gun arabic, which is subsequently removed when the master cylinder or moisture roller, as the case maybe, isv put into service.

DESCRIPTION OF PREFERRED EMBODIMENTS A master cylinder or moisture fountain roll of. co n ventionalshape is formed in; the conventional manner. A master cylinder will usually be made of castiron, and a fountain roll of steel. In accordance with the invention the cylinder (whether master cylinder or fountain roll) may be provided with a-tin-nickel surface by the following plating process. I I

' The cast iron cylinder is first degreased 'with trichlorethylene and then anodically cleaned in a caustic bath containing metasilicate and a wetting agent, in a mild steel tank, applying a current of 1 00 ampslsqft. for 2-3 minutes, and maintaining a temperature of 175- 200 F. The cylinder is then swilled in cold running water, pickled in cold 50percent hydrochloric acid for k 1 minute and again swilled in cold running water.

The cylinder is then copper plated in a copper cyanide bath using 6 oz. per imperial gallon copper cyanide with 3 oz. per imperial gallon potassium cyanide in a mild steel tank, a temperature of F. and a current density of 25-50 ampslsqft. Agitation is effected by rocking the cathode. Plating is stopped when 0.0002 inch to 0.0003 inch thickness of copper has been obtained and the cylinder is then swilled twice in cold running water.

The cylinder is subsequently tin-nickel plated from a bath of the following composition in a tank with a lining of low sulphur hard rubber:

. Stannous Chloride 8 oz. Nickel Chloride 40 50 oz. Ammonium Bifluoride 6 oz. pH 1.5 2.5

The anodes are of 65/35 tin-nickel, polypropylenebagged. A temperature of 160 170F. is used, with an anode current density of over 50 amps/sq.ft. and a cathode density under 25 amps/sq.ft. (to avoid pitting in high current density areas), and a voltage of 3-4 volts. The bath is agitated by longitudinally rocking the cathode. A plating time of 20 minutes gives a thickness of .006 0.007 inch. The plated cylinder is removed to a rubber-lined drag out tank the contents of which are used to make up the bath. The plated cylinder is then given a static hot water swill containing lb. per 100 imperial gallons, sodium nitrate to prevent rust.

As is well known in connection with the plating processes of this character, the resulting deposit of the metals is in an approximate equi-atomic ratio. In this case the deposit will contain approximately 67 percent tin and 33 percent nickel. Unless the electrolyte or plating conditions are allowed to become grossly out of balance, the ratio of the metals will not vary more than a few per cent from the above stated value, say in the range of about 62 percent'tin and 38 percent nickel, to 72 percent tin and 28 percent nickel, and for the pur: poses of this description and the subjoined claims, the expression equi-atomic ratio will be understood to identify alloys within the range of ratios in which tin and nickel would normally automatically deposit when electrolytically plated as herein described.

No jigging of the cylinder is required.

No back etching or flash plating is required.

The cylinder, when all plating operations are completed, and while still wet, is coated with a solution of gum arabic, to guard against accidental abrasion and to preserve the hydrophilic nature of the surface.

When a tin-nickel plated master cylinder or fountain roll is installed in a lithographic printing machine and the machine is to be put into service, the cylinder or roll surface is prepared by wiping it with 5 percent nitric acid with excess Vienna lime (calcium and magnesium carbonates), or the like.

The master cylinder or fountain roll should when in use be cleaned with a similar solution once a day.

A field test has been carried out with a series of similar lithographic printing machines employing photographic master preparations, some of the machines having a conventional hard chromium plated matter cylinder and others a tin-nickel plated cylinder as above described. The machines were given similar use side by side. The chromium cylinders had an average life of 4 months. The tin-nickel cylinders lasted for l2 to 24 months. The cost of the tin-nickel cylinders is about half that of the chromium cylinders.

The preferred range of copper under-plating is 0.0002 to 0.0005 inch. The preferred range for the tinnickel plating is 0.0004 to 0.00l5 inch: for the moisture rolls the upper end of this range is preferred, say, 0.0009 to 0.0015 inch, while for master cylinders the lower end of the range, say 0.0004 to 0.0010 inch suffices. Plating thickness is varied by varying the plating time.

For moisture rolls a tin-nickel surface has the advantage that it picks up a very uniform moisture layer which makes for more even wetting of the master cylinder. Also, the tedious frequent cleaning of the hitherto used aluminium rolls is avoided.

What is claimed is:

l. A lithographic printing machine comprising a master cylinder for receiving a master whose image areas attract oleaginous ink and a moisture system, including a repellent fountain, a fountain roll, and a repellent train including one or more rolls for taking aqueous repellent solution from the fountain and applying it to the surface of a master on said master cylinder, in which at least one of said cylinder, fountain roll and fountain train rolls has a surface of an alloy of tin and nickel in equi-atomic ratio.

'2. A method of lithographic duplicating which com prises providing a master cylinder with a surface of an alloy of tin and nickel in an equi-atomic ratio, applying a master to the surface of said master cylinder, applying an aqueous repellent solution and an oleaginous ink to the surface of the master cylinder and the master thereon, and making impressions on copy sheets from the thus inked master.

3. A method of lithographic duplicating which comprises applying a master to a master cylinder, providing a moisture system including a fountain roll, providing said fountain roll with a surface of an alloy of tin and nickel in an equi-atomic ratio, applying an aqueous repellent solution to the surface of said master by means of said moisture system, and applying an oleaginous ink to the surface of the master on the master cylinder and making impressions on copy sheets from the thus inked master.

4. A method of lithographic duplicating which comprises applying a master to a master cylinder, providing a moisture system including a fountain roll and a repellent train including one or more rolls, providing on at least one of said rolls a surface of an alloy of tin and nickel in an equi-atomic ratio, applying an aqueous repellent solution to the surface of said master by means of said moisture system, and applying an oleaginous ink to the surface of the master on the master cylinder and making impressions on copy sheets from the thus inked master. 

1. A LITHOGRAPHIC PRINTING MACHINE COMPRISING A MASTER CYLINDER FOR RECIEVING A MASTER WHOSE IMAGE AREAS ATTRACT OLEAGINOUS INK AND A MOISTURE SYSTEM, INCLUDING A REPELLENT FOUNTIAN, A FOUNTAIN ROLL, AND A REPELLENT TRAIN INCLUDING ONE OR MORE ROLLS FOR TAKING AQUEOUS REPELLENT SOLUTION FORM THE FOUNTAIN APPLYING IT TO THE SURFACE OF A MASTER ON SAID MASTER CYLIDER, IN WHICH AT LEAST OF OF SAID CYLINDER, FOUNTIAN ROLL AND FOUNTAIN TRAIN ROLLS HAS A SURFACE OF AN ALLOY OF TIN AN NICKLE IN AQUI-ATOMIC RATIO.
 2. A method of lithographic duplicating which comprises providing a master cylinder with a surface of an alloy of tin and nickel in an equi-atomic ratio, applying a master to the surface of said master cylinder, applying an aqueous repellent solution and an oleaginous ink to the surface of the master cyLinder and the master thereon, and making impressions on copy sheets from the thus inked master.
 3. A method of lithographic duplicating which comprises applying a master to a master cylinder, providing a moisture system including a fountain roll, providing said fountain roll with a surface of an alloy of tin and nickel in an equi-atomic ratio, applying an aqueous repellent solution to the surface of said master by means of said moisture system, and applying an oleaginous ink to the surface of the master on the master cylinder and making impressions on copy sheets from the thus inked master.
 4. A method of lithographic duplicating which comprises applying a master to a master cylinder, providing a moisture system including a fountain roll and a repellent train including one or more rolls, providing on at least one of said rolls a surface of an alloy of tin and nickel in an equi-atomic ratio, applying an aqueous repellent solution to the surface of said master by means of said moisture system, and applying an oleaginous ink to the surface of the master on the master cylinder and making impressions on copy sheets from the thus inked master. 